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Submarine freshwater springs in the Adriatic Sea: a unique habitat of the bryozoan Pentapora fascialis

Large colonies of the bryozoan Pentapora fascialis (Pallas, 1766) growing inside the plume of submarine freshwater springs (vruljas) have been surveyed. In the Velebit Channel, P. fascialis grows only under the influence of a vrulja's outflow, at depths from 1 m to 35 m. We have investigated the water chemical composition and temperature of each vrulja's plume. The amount of nutrients, carbonates, and temperature of the vruljas' plumes were measured during three different seasons in 2002 and 2003. All measured nutrients had considerably higher concentrations inside the vruljas than in the seawater (9.185 +/- 7.111 mmol/m3 NO3- in vruljas and 1.109 +/- 0.949 mmol/m3 NO3- in the seawater ; 7.911 +/- 8.316 mmol/m3 SiO4 in vruljas and 1.643 +/- 1.330 mmol/m3 SiO4 in the seawater ; 1.757 +/- 1.496 mmol/m3 NH4+ in vruljas and 1.141 +/- 1.299 mmol/m3 NH4+ in the seawater ; 0.116 +/- 0.119 mmol/m3 NO2- in vruljas and 0.105 +/- 0.106 mmol/m3 NO2- in the seawater and 0.102 +/- 0.189 mmol/m3 PO43- in vruljas and 0.025 +/- 0.013 mmol/m3 PO43- in the seawater). Furthermore, the amount of total CO2, HCO3- and dissolved CO2 was higher inside the plume (2.570 +/- 0.436 mmol/l total CO2 in vruljas and 2.270 +/- 0.441 mmol/l total CO2 in the seawater ; 2.431 +/- 0.479 mmol/l HCO3- in vruljas and 2.003 +/- 0.549 mmol/l HCO3- in the seawater and 0.044 +/- 0.034 mmol/l dissolved CO2 in vruljas and 0.017 +/- 0.012 mmol/l dissolved CO2 in the seawater), while CO32- had lower values inside vruljas' plumes than in the seawater (0.098 +/- 0.075 mmol/l CO32- in vruljas and 0.202 +/- 0.081 mmol/l CO32- in the seawater). The temperature of the vruljas' outflow was low and constant throughout the year and varied between 9.76 and 14.02°C, while the seawater temperature at 23 m varied between 8.22 and 23.52°C. The period of vruljas' inactivity was only 5.6 days per year which means that P. fascialis must be permanently adapted to grow in the conditions of fluctuating, lower salinity.

Bryozoa, Pentapora fascialis, Adriatic Sea, vruljas

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